JP2005307807A - Internal egr amount estimating device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately estimate internal EGR amount by reflecting influence of blowing-through gas in an engine in which an intake valve opening period and an exhaust valve opening period are overlapped. <P>SOLUTION: At least pressure in a cylinder Pcyl and amount of suction air Qair are detected as a condition in the cylinder in an intake valve closing period IVC to calculate internal EGR amount MRES based on the detected pressure in the cylinder Pcyl. Preferably, temperature in the cylinder Tcyl and effective process volume Vstr in the intake valve closing period IVC are detected in addition to them to reflect in the calculation of the internal EGR amount MRES. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an internal EGR amount estimation device for an engine, and more particularly to a technique for estimating an internal EGR amount of an engine in which an intake valve opening period and an exhaust valve opening period overlap.

Conventionally, in an engine, exhaust gas recirculation (hereinafter referred to as “EGR”) for returning a part of exhaust gas into a cylinder is performed in order to suppress generation of nitrogen oxides due to an increase in combustion temperature.
The EGR includes an external EGR that is performed via an EGR pipe connected between an exhaust pipe and an intake pipe, and an internal EGR that is performed without passing through the EGR pipe. Among these, the following is known as an apparatus for estimating the amount of recirculated gas by external EGR (Patent Document 1). The intake pipe pressure and engine speed during the intake stroke are detected, and the total intake gas amount into the cylinder is calculated based on the detected intake pipe pressure and engine speed, while the air flow installed in the intake passage First-order lag processing is applied to the meter output, and the intake air amount per cycle is calculated. The amount of recirculation gas is calculated by subtracting the amount of intake air from the calculated total amount of intake gas.
Japanese Patent Application Laid-Open No. 06-330821 (paragraph numbers 0037 to 0043)

  In order to further increase the output, an engine in which the charging efficiency is increased by overlapping the intake valve opening period and the exhaust valve opening period in a predetermined operating region is known. In this engine, the amount of exhaust gas recirculated by the internal EGR (that is, the internal EGR amount) is accurately estimated, including the exhaust gas that blows from the exhaust side to the intake side during the overlap period (hereinafter referred to as “blow-off gas”). It is desired to reflect the result in engine control such as fuel injection control. Here, the above apparatus is applied to the estimation of the recirculation gas amount by the external EGR, but cannot be applied to the estimation of the internal EGR amount substantially. The above device calculates the total intake gas amount by paying attention to the unambiguous relationship with the intake pipe pressure and the engine speed, and the influence of the blown-out gas can be reflected on the calculated total intake gas amount. This is because the amount of internal EGR cannot be accurately estimated.

  An object of the present invention is to accurately estimate an internal EGR amount in an engine in which an intake valve opening period and an exhaust valve opening period overlap with each other, reflecting the effect of blowout gas.

  The present invention provides an internal EGR amount estimation device for an engine. The apparatus according to the present invention is provided in an engine in which an intake valve opening period and an exhaust valve opening period overlap. In the first embodiment, the flow rate of air sucked into the cylinder is detected, the cylinder pressure during the intake stroke is detected, and the internal EGR amount of the engine is determined based on at least the detected flow rate and cylinder pressure. calculate. In the second embodiment, the intake air amount per cycle is detected, the in-cylinder pressure during the intake stroke is detected, and the internal EGR amount of the engine is determined based on at least the detected intake air amount and in-cylinder pressure. calculate.

  According to the present invention, the flow rate of air sucked into the cylinder or the amount of intake air per cycle is detected, the cylinder pressure during the intake stroke is detected, and the detected flow rate and the cylinder pressure are detected. In addition, since the internal EGR amount is calculated, the internal EGR amount can be calculated based on the in-cylinder state after the exhaust blowout occurs, and the internal EGR amount is reflected to reflect the influence of the blown-out gas. The quantity can be estimated accurately.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration of an engine 1 according to an embodiment of the present invention.
An air cleaner 12 is attached to the introduction portion of the intake passage 11, and dust or the like in the intake air is removed by the air cleaner 12. In the intake passage 11, an electronically controlled throttle valve 13 is installed downstream of the air cleaner 12. A surge tank 14 is attached downstream of the throttle valve 13, and a branch 15 is attached to the surge tank 14 to constitute an intake manifold. The intake air in the surge tank 14 flows into the cylinder through the branch 15 and the intake port 16 formed in the cylinder head. A fuel supply injector 17 is installed in the intake port 16 of each cylinder.

  In the engine body, the combustion chamber 18 is formed as a space sandwiched between the cylinder head and the piston 19. The combustion chamber 18 is connected to the intake port 16 on one side with respect to the cylinder center axis, and the intake port 16 is opened and closed by the intake valve 20. The intake valve 20 is driven by an intake cam 21. In addition, the combustion chamber 18 is connected to the exhaust port 22 on one side opposite to the intake port 16, and the exhaust port 22 is opened and closed by an exhaust valve 23. The exhaust valve 23 is driven by an exhaust cam 24. An intake side variable valve device 25 is provided for the intake cam 21, and an exhaust side variable valve device 26 is provided for the exhaust cam 24, and the intake cam 21 or the exhaust cam is provided by these variable valve devices 25, 26. The operation characteristic of the intake valve 20 or the exhaust valve 23 can be changed by changing the phase of each of the 24 camshafts. The variable valve operating devices 25 and 26 may be of any type such as a hydraulic type or a solenoid type. In this embodiment, the opening / closing timing of the intake valve 20 or the exhaust valve 23 (that is, the valve timing) is determined. By changing, an overlap period between the intake valve opening period and the exhaust valve opening period (hereinafter simply referred to as “overlap period”) is adopted. A spark plug 27 is installed in the cylinder head so as to face the substantially upper center of the combustion chamber 18.

A first catalytic converter 29 is interposed in the exhaust passage 28 immediately after the exhaust manifold, and a second catalytic converter 30 is interposed downstream thereof. The exhaust gas flowing out to the exhaust port 22 passes through the catalytic converters 29 and 30 and the muffler 31 and is released into the atmosphere.
The operations of the injector 17, the spark plug 27 and the variable valve gears 25 and 26 are controlled by an electronic control unit (hereinafter referred to as “ECU”) 41 as an engine control unit. The ECU 41 has an intake flow rate detection signal from the air flow meter 51, a manifold pressure detection signal from the pressure sensor 52, a coolant temperature detection signal from the temperature sensor 53, a unit crank angle and a reference crank angle detection signal from the crank angle sensor 54. (The ECU 41 calculates the engine speed NE based on this), an exhaust pressure detection signal from the pressure sensor 55, an exhaust temperature detection signal from the temperature sensor 56, an air-fuel ratio detection signal from the oxygen sensor 57, The accelerator opening detection signal from the accelerator sensor 58 and the cam angle detection signals from the cam angle sensors 59 and 60 (based on this, the actual phase difference between the cam and the camshaft can be detected) are input. Is done. The ECU 41 sets the control amount of each device described above based on each input signal. In the present embodiment, the temperature sensor for detecting the intake air temperature Tint is configured integrally with the air flow meter 51.

In the present embodiment, the ECU 41 has a function as an internal EGR amount estimation device of the engine 1.
Hereinafter, estimation of the internal EGR amount MRES by the ECU 41 will be described.
The recirculation gas by the internal EGR according to the present embodiment includes exhaust that blows from the exhaust side to the intake side during the overlap period (that is, blow-out gas) and exhaust that remains in the cylinder after the exhaust valve closing timing EVC. It is.

In this embodiment, the in-cylinder state at the intake valve closing timing IVC is estimated, and based on this, the internal EGR amount MRES is calculated.
FIG. 2 is a flowchart of an internal EGR amount estimation routine. This routine is executed every cycle in synchronization with the reference crank angle signal. In this routine, the residual gas ratio Rrst, and hence the internal EGR amount MRES, is calculated based on the in-cylinder state at the intake valve closing timing IVC.

  In S101, the rotational position of the crankshaft (hereinafter referred to as “crank angle”) CA is calculated based on the reference crank angle signal and the unit crank angle signal. The reference crank angle signal is output once for each cylinder during one rotation of the crankshaft, indicating that the target cylinder is at a predetermined reference position. On the other hand, the unit crank angle signal is output every time the crankshaft rotates by a unit angle (for example, 1 °).

  In S102, the cylinder pressure Pcyl is read. This in-cylinder pressure Pcyl refers to the in-cylinder pressure at the intake valve closing timing IVC, and is approximated by the manifold pressure Pint at the same time. This manifold pressure Pint will be described later, assuming that the pressure fluctuation due to pulsation DPpul is added to the manifold pressure Pmani (calculated as an average pressure during the intake stroke) calculated based on the output of the pressure sensor 52. It is detected by an intake pressure detection routine.

In S103, the in-cylinder temperature Tcyl is read. This in-cylinder temperature Tcyl refers to the in-cylinder temperature at the intake valve closing timing IVC, and is detected by a later-described in-cylinder temperature detection routine.
In S104, an effective stroke volume Vstr is calculated. In the target cylinder, if the crank angle CA at the timing when the piston 19 is at the top dead center is set to 0, the effective stroke volume Vstr is calculated by the following equation. In the following formula, the bore cross-sectional area is Abore, the effective stroke length is Lstref, and the total stroke length between the top dead center and the bottom dead center is Lstr.

Vstr = Abore × Lstreff (1.1)
Lstreff = (Lstr / 2) × (1+ | cosCA |) (1.2)
In S105, the intake air amount Qcyl is read. The intake air amount Qcyl refers to the amount of air that is taken into the target cylinder per cycle, and is calculated by integrating the intake air flow rate Qair over the intake stroke in an intake air amount detection routine (not shown).

In S106, a residual gas ratio Rrst is calculated. The residual gas ratio Rrst is calculated by the following equation based on the in-cylinder pressure Pcyl, the in-cylinder temperature Tcyl, the effective stroke volume Vstr, and the intake air amount Qcyl read or calculated as described above.
Rrst = 1− (Qcyl × Tcyl) / (Vstr × Pcyl) (2)
In S107, the internal EGR amount MRES is calculated. The internal EGR amount MRES is calculated according to the following equation, assuming that the value obtained by subtracting the residual gas rate Rrst from 1 gives the ratio of the intake air amount Qcyl to the total intake gas amount.

MRES = (Rrst / (1-Rrst)) × Qcyl (3)
The internal EGR amount MRES calculated as described above is reflected in the fuel injection control by the injector 17 and the ignition control by the spark plug 27.
FIG. 3 is a flowchart of an intake pressure detection routine. This routine is executed every predetermined time. In this routine, the cylinder pressure Pcyl at the intake valve closing timing IVC is approximated by the manifold pressure Pint in the same period.

  The ECU 41 stores a tuning order table shown in FIG. 4 and a pulsation pressure ratio table shown in FIG. The ECU 41 calculates a change amount DNE of the tuning rotation speed NEK according to actual operating conditions (here, the intake air temperature Tint), and shifts and shifts the pulsation pressure ratio RPpul with respect to the engine rotation speed NE by the calculated change amount DNE. The actual pulsation pressure ratio RPpul is calculated with reference to the pulsation pressure ratio table after the operation. The calculated pulsation pressure ratio RPpul is converted into a pulsation correction value DPint, and this is added to the detected manifold pressure Pmani. The manifold pressure at the intake valve closing timing IVC (the pressure fluctuation due to pulsation is taken into consideration with respect to the manifold pressure Pmani). Pint, that is, in-cylinder pressure Pcyl is calculated.

Here, a supplementary explanation will be given for each of the above tables.
The tuning order table is set by correcting the theoretical expression of the tuning order Mint0 at the reference intake air temperature (for example, Tint = 25 ° C.) according to the result of calculation or experiment. A straight line L1 indicated by a dotted line in FIG. 4 indicates the reciprocal of the theoretical tuning order Mint0 at the reference intake air temperature, and is expressed by the following equation.

1 / Mint0 = (1 / (120 × Fint)) × NE (4)
In the equation (4), the fundamental frequency of the air column vibration in the intake passage is Fint, and this fundamental frequency Fint is calculated by the following equation, where the equivalent pipe length of the intake passage is Le and the sound speed is Spsd. In Equation (6), the actual pipe length of the intake passage is Lint, and the open end correction value is DL. In the equation (7), the specific heat ratio is κair and the gas constant is Rair.

Fint = Spsd / (2 × Le) (5)
Le = 2 (Lint + DL) (6)
Spsd = √ {κair × Rair × Tint} (7)
The manifold pressure Pmani is detected and plotted for each engine speed, and the engine speed NEa1 at the point P1 corresponding to the tuning order Mint = A is read from the obtained curve C1 (FIG. 5). In FIG. 4, the engine speed NEa0 corresponding to 1 / Mint0 = 1 / A on the straight line L1 is read, and the slope of the theoretical formula (4) is corrected by the following formula (straight line L2). Note that the engine speed NEa1 at the point P1 can also be specified based on the manifold pressure obtained by desktop calculation.

1 / Mint = (1 / (120 × Fint)) × (NEa0 / NEa1) × NE (8)
The equation (8) thus obtained is tabulated and stored in the ECU 41 as a tuning order table. The characteristics of the tuning order Mint may be stored as a function instead of the table.

  On the other hand, the pulsation pressure ratio table is set as follows. Assuming that the engine 1 is in an equilibrium state with respect to temperature and the intake air temperature and the outside air pressure are the reference intake air temperature and the atmospheric pressure, respectively, the manifold pressure Pincl in consideration of the pulsation at the intake valve closing timing IVC is calculated by the desktop calculation. Know by number. The deviation of the obtained manifold pressure Pincl from the detected manifold pressure Pmani is tabulated as a pulsation pressure ratio RPpul and stored in the ECU 41.

RPpul = (Pincl−Pmani) / Pmani (9)
In S201, the intake air temperature Tint, the manifold pressure Pmani, and the engine speed NE are read.
In S202, a tuning rotational speed NEK under actual operating conditions is calculated. A tuning order characteristic line (L3 in FIG. 4) at the read intake air temperature Tint (for example, 70 ° C.) is calculated by the equations (5) to (8), and 1 / Mint = 1 / A on the calculated characteristic line. The engine speed NEa2 corresponding to is calculated as the tuning speed NEK. The tuning order Mint employed when calculating the tuning rotational speed NEK is selected in consideration of the practical operation range.

In S203, a difference DNE between the tuning rotational speed NEK (= NEa2) and the engine rotational speed NEa1 with the tuning order Mint being A under the reference intake air temperature is calculated, and the calculated pulsation pressure ratio table (FIG. 6) is calculated. Shift by DNE.
In S204, the pulsation correction value DPint is calculated using the shifted pulsation pressure ratio table (hereinafter referred to as “correction pulsation pressure ratio table”). The pulsation correction value DPint is calculated by reading the pulsation pressure ratio RPpul corresponding to the current engine speed NE from the correction pulsation pressure ratio table, and multiplying the read pulsation pressure ratio RPpul by the manifold pressure Pmani.

DPint = RPpul × Pmani (10)
In S205, the intake air pressure Pint is calculated by adding the manifold pressure Pmani to the calculated pulsation correction value DPint.
Pint (= Pcyl) = Pmani + DPint (11)
FIG. 7 is a flowchart of the in-cylinder temperature detection routine. This routine is executed every predetermined time. In this routine, the in-cylinder temperature Tcyl at the intake valve closing timing IVC is approximated by the exhaust temperature Texh at the exhaust valve closing timing EVC.

In S301, the crank angle CA and the exhaust temperature Texh are read.
In S302, based on the read crank angle CA, it is determined whether or not the exhaust valve closing timing EVC is reached. When the exhaust valve closing timing EVC is reached, the routine proceeds to S303, and when not, this routine is returned.
In S303, the exhaust temperature Texh at the exhaust valve closing timing EVC is held as the in-cylinder temperature Tcyl at the intake valve closing timing IVC.

  In this embodiment, S105 in the flowchart shown in FIG. 2 is the intake air amount detection means, S102 (the whole flowchart shown in FIG. 3) in the flowchart is the in-cylinder pressure detection means (S201 in the flowchart shown in FIG. 3 is the intake pressure detection). 2, S202 to 204 in the flowchart constitute pulsation correction value calculation means. S106 and 107 in the flowchart shown in FIG. 2 represent internal EGR amount calculation means, and S103 in the flowchart (shown in FIG. 7). The entire flow chart) constitutes the in-cylinder temperature detection means (S301 in the flow chart shown in FIG. 7 constitutes the exhaust temperature detection means), and S104 in the flow chart shown in FIG. 2 constitutes the stroke volume detection means.

According to this embodiment, the following effects can be obtained.
First, the intake air amount Qair per cycle is detected, the in-cylinder pressure Pcyl at the intake valve closing timing IVC is detected, and the internal EGR amount is calculated based on the detected intake air amount Qair and the like. Therefore, the internal EGR amount can be calculated based on the in-cylinder state after the exhaust blowout occurs, and the internal EGR amount can be accurately estimated by reflecting the influence of the blown-out gas. .

Second, since the in-cylinder pressure Pcyl is approximated by the intake pressure Pint at the intake valve closing timing IVC, the in-cylinder pressure Pcyl can be easily detected.
Third, when detecting the in-cylinder pressure Pcyl, a pulsation pressure ratio table at the reference intake air temperature is set, and this table is shifted according to the intake air temperature Tint during actual operation, and the table after the shift is referred to. Thus, since the pulsation correction value DPint is calculated, it is not necessary to create a pulsation pressure ratio table for each different temperature, and the number of man-hours for control can be reduced.

  Fourth, since the in-cylinder temperature Tcyl and the effective stroke volume Vstr of the piston 19 at the intake valve closing timing IVC are detected, the internal EGR amount is calculated in consideration of the detected in-cylinder temperature Tcyl and the like. The amount of internal EGR can be estimated more accurately. In particular, when the effective stroke volume Vstr is considered, when the intake valve closing timing IVC is changed by the intake side variable valve operating device 25 and the substantial stroke volume is changed, the internal EGR amount is correspondingly changed. It can be estimated accurately.

Fifth, since the exhaust temperature Texh is detected and the in-cylinder temperature Tcyl is approximated by the exhaust temperature Texh at the exhaust valve closing timing EVC, the in-cylinder temperature Tcyl can be easily detected.
In the above description, the average pressure during the intake stroke is used as the manifold pressure Pmani used for calculating the in-cylinder pressure Pcyl. However, the present invention is not limited to this, and is detected by the pressure sensor 52 at a predetermined timing during the intake stroke. The in-cylinder pressure Pcyl may be calculated by using the instantaneous pressure as the representative pressure.

In the above, the case where the cam profile itself is constant and the overlap period is changed by changing only the valve timing has been described as an example, but not limited to this, the overlap period is changed with the cam profile change. It may be changed.
Further, the pulsation pressure ratio table (FIG. 6) may be created and set for each opening degree of the throttle valve 13.

Configuration of engine according to one embodiment of the present invention Flow chart of internal EGR amount estimation routine Flow chart of intake pressure detection routine Tuning order table Relationship between engine speed NE and manifold pressure Pmani Pulsating pressure ratio table In-cylinder temperature detection routine flowchart

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 11 ... Intake passage, 12 ... Air cleaner, 13 ... Throttle valve, 16 ... Intake port, 17 ... Injector, 18 ... Combustion chamber, 19 ... Piston, 20 ... Intake valve, 21 ... Intake cam, 22 ... Exhaust port , 23 ... exhaust valve, 24 ... exhaust cam, 25 ... intake side variable valve operating device, 26 ... exhaust side variable valve operating device, 27 ... ignition plug, 28 ... exhaust passage, 41 ... engine control unit, 51 ... air flow meter, 52 ... Manifold pressure sensor, 53 ... Cooling water temperature sensor, 54 ... Crank angle sensor, 55 ... Exhaust pressure sensor, 56 ... Exhaust temperature sensor, 57 ... Oxygen sensor, 58 ... Accelerator sensor, 59, 60 ... Cam angle sensor.

Claims (8)

Provided in the engine where the intake valve opening period and the exhaust valve opening period overlap,
Means for detecting the flow rate of air sucked into the cylinder;
Means for detecting in-cylinder pressure during the intake stroke;
An engine internal EGR amount estimation device comprising: means for calculating an internal EGR amount of the engine based on at least the detected flow rate and in-cylinder pressure. Provided in the engine where the intake valve opening period and the exhaust valve opening period overlap,
Intake air amount detection means for detecting the intake air amount per cycle;
In-cylinder pressure detecting means for detecting the in-cylinder pressure during the intake stroke;
An internal EGR amount estimation device for an engine configured to include an internal EGR amount calculation means for calculating an internal EGR amount of the engine based on at least the detected intake air amount and in-cylinder pressure.   3. The internal EGR amount estimating device for an engine according to claim 2, wherein the internal EGR amount calculating means calculates the internal EGR amount based on the in-cylinder pressure at the intake valve closing timing. An intake pressure detecting means for detecting a representative or average pressure of the intake pressure;
It has a basic pulsation correction value for each engine speed related to the intake air pressure set at the reference temperature. A pulsation correction value calculation means for calculating a pulsation correction value,
4. The engine internal EGR amount estimating device according to claim 2, wherein the in-cylinder pressure detecting means detects the in-cylinder pressure by correcting the detected intake pressure with the calculated pulsation correction value. It further includes in-cylinder temperature detecting means for detecting the in-cylinder temperature during the intake stroke,
The internal EGR amount calculation means according to any one of claims 2 to 4, wherein the internal EGR amount calculation means calculates the internal EGR amount based on the detected intake air amount, in-cylinder pressure and in-cylinder temperature. . An exhaust gas temperature detecting means for detecting the exhaust gas temperature is further included.
6. The engine internal EGR amount estimation device according to claim 5, wherein the in-cylinder temperature detecting means estimates and detects the in-cylinder temperature based on the detected exhaust gas temperature.   The engine internal EGR amount estimation device according to claim 6, wherein the in-cylinder temperature detecting means estimates the in-cylinder temperature based on the exhaust temperature at the exhaust valve closing timing. And further comprising stroke volume detecting means for detecting a substantial stroke volume of the piston,
The internal EGR amount calculating means calculates the internal EGR amount based on the detected intake air amount, in-cylinder pressure, in-cylinder temperature, and stroke volume, according to any one of claims 5 to 7. Quantity estimation device.

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